THE GEXirs EQUrSETlTM. ]7| 



rogenous tissue had ^-iven rise to spore-mothers ami too Httle to the fonnatioii of ta[)etal 

 cells, and, as a consequence, the resultant spores produced only depauperate plants. A 

 series of observations in this dii-ectiou uiiglit prove interesting in connection with Bower's 

 theory of the origin of tlie sporopliyte. PI. 2G, figs. 12 and 13, sufficiently illustrate the 

 external features of the young sporopliytes of E. /imnsinii, and show that they do not 

 differ essentially from those of U. likmale, except in their greater delicacy, and in the 

 smaller number of segments formed in the first shoot. 



Turning our attention now to the internal development of E. /ilciiifiic, we {\\u\ that 

 in the first axis of the young sporopliyte there is a gradual ti'ansition from the typical 

 arrangement ol the tissues in the root, to that obtaining in the base of the youni;- stem. 

 The central cylinder of the first shoot makes its appearance as an unbrokeu tube of 

 reticulated tracheides. There are no typical protoxylem elements, although the internal 

 tracheides are formed first. The jirimitive vascular axis, in fact, starts out with a similar 

 organization to that which is found subsequently to recur at the nodes. The center of the 

 vascular tube is occupied by })arenchyma, which may be considered in the light of what is 

 to follow, as belonging to the pericycle. Outside the ring of reticulated vessels occurs a 

 zone of phloem, terminated by a typical eiidodernns. with the usual radial ligiiilied hands. 

 The rndhnent of the second shoot causes an interrui)tion in the continuity of the vas- 

 cidar cyliniler of the primary axis aliove its point of origin which disappears again, at 

 about the level of exit of the leaf-traces from the central cylinder. The latter do not 

 cause any gaps in the vascular ring as they pass off, and it is only at a measuralile dis- 

 tance above their points of origin, that the so-called foliar lacunae make their appearance. 

 The first slioot-bud originates between two leaf-traces as do all the subsequent ones. The 

 foliar lacunae described above, if they may so be called, divide the fibrovascular tulje into 

 three distinct strands which alternate with the leaves. These three strands differ from 

 the woody ring below in having typical protoxjlem elements, which lie in more or less 

 characteristic carinal lacunae. They are surrounded by a common external endodermis. 

 At a point two or three millimeters above the e.xit of the leaf-traces of the primar\' whorl, 

 a cell makes its appearance in the midst of the internodal bundles, which is cliaracteriz(!d 

 by having endodernial markings on its walls; still higher up this gives j^lace to a radiating 

 group of cells, which have endodernial dots about the middle of their radial walls. Just 

 above the exit of the leaf-traces of the ne.xt whorl, that is at the base of the next inter- 

 node, the internal endodernial elements disajjpear. They again become evident at a short 

 distance above this point, only to disappear again above the exit of the leaf-traces of the 

 next intei'node. These variations recur in all the segments of the first shoot and need not 

 be further descrilted. In the higher internodes, however, the internal endodermis shows a 

 tendency to unite with the outer one, just below the continuous rings of reticulate vascu- 



